Transmission system



June 22, 1937. Y L, SCHQTT 2,084,457

TRANSMISS ION SYSTEM Filed Aug. 2, 1955 ilumnm any AAA A A A I l A I V IAVAVAV%I).VIIIV DELAY CIRCUIT //v l/EN TOR L. StHOTT A TTQRA/Ei Patented June 22, 1937 UNITED STATES PATENT GFFEQE TRANSMISSION SYSTEM Application August 2,

10 Claims.

This invention relates to signal transmission systems and particularly to volume control circuits for signal transmission systems.

One object of the invention is to provide a four-wire section. of a transmission system with a single control circuit that shall govern volume compression means in the transmitting line and volume expansion means in the receiving line.

Another object of the invention is to provide a four-wire section of a transmission system with a control circuit connected to the transmitting and receiving lines by a hybrid coil that shall govern volume compression means in the transmitting line and volume expansion means in the receiving line.

Another object of the invention is toprovide a four-wire section of a transmission system with a control circuit connected to the transmitting and receiving lines that shall govern compression means in the transmitting line to effect compression of the volume range of the signals beyond the compression means with respect to the volume range of the signals before the compression means according to a fixed ratio and that shall govern expansion means in the receiving line to effect expansion of the volume range of the signals beyond the expansion means with respect to the volume range of signals before the expansion means according to a fixed ratio.

A further object of the invention is to provide a four-Wire section of a transmission system with a control circuit of the above indicated type and with blocking means that shall block the output circuit of the compressor in the transmitting line when the receiving line is in use and that shall block the output circuit of the expandor in the receiving line when the transmitting line is in use.

The volume range of signals is, in many instances, larger than can be efliciently transmitted over a line. Satisfactory transmission of signals over a line has an upper limit to avoid overloading of line apparatus, such as repeaters,

; and has a lower limit by reason of interference from line noises. In order to transmit signals over a, line with a volume range between the upper and lower limits, it is customary to compress the volume range of the signals at the sending end of the line and to expand the volume range of the signals at the receiving end of the line.

The present invention has been illustrated by means of the volume compression and the volume expansion circuits disclosed in the patent to 1935, Serial No. 34,455

Stephen Doba, Jr., No. 2,018,489,-dated October 22, 1935. The present invention, which is applicable to a four-wire transmission line, is provided with a single rectifying control circuit for not only governing the volume range compressing means in the transmitting line but also for governing the volume range expanding means in the receiving line.

In the transmission system employed to describe the present invention, atwo-wire transmission line is connected to one end of a fourwire transmission circuit by means of a hybrid coil. The transmitting line of the four-wire circuit is provided with a gain adjusting device of any suitable type. A gain adjusting device of any suitable type is also provided in. the receiving line of the four-wire section. The four-wire section is also provided with echo suppressor circuits of the type disclosed in D. Mitchell Patent No. 1,986,515, dated January 1, 1935. A compressor of the type disclosed in the patent to Stephen Doba, Jr., No. 2,018,489, dated October 22, 1935, is provided in the transmitting line. This compressor preferably comprises an impedance pad having two space discharge devices in push-pull relation connected across it as the shunt member. The receiving line of the fourwire section is provided with an expandor of the type disclosed in the above mentioned patent to Stephen Doba, Jr. This expandor preferably comprises two space discharge devices in pushpull relation effectively connected in series with the receiving line.

A single rectifying control circuit is provided at each end of the four-wire section of the transmission system for controlling a volume compressor in'one line and a volume expander in the other line. The rectifying circuit which is of the type shown inthe Doba application for controlling either the compressor or the expander, is connected to the transmitting line and thereceiving line of the four-wire section of the transmission system by means of a suitable hybrid coil. The hybrid coil is connected to the transmitting line beyond the compressor and is connected to the receiving line before the expandor. The rectified potential supplied by the rectifying circuit controls the grid bias on the space discharge devices connected across the pad in the transmitting line and the grid bias on the two space discharge devices effectively connected in series with" the receiving line. The characteristic of the rectifying circuit has a definite relation with respect to the characteristic of the compressor so that the volume range of the signals on the transmitis preferably of the space discharge. type. The

ting line beyond the compressor are compressed before the compressor according to a fixed ratio. a

volume range ofthe signals before according to a fixed ratio.

with respect to the volume range of the signals The characteristic of the rectifying circuit also bears a definite relationwith respect to the charact'eristic of the space discharge devices in the expandor to expand'the volume range of the signals beyond the expandor With'respect to the the receiving line .is m service. A similarrelay is provided for blocking the outputof the'expandor in the receiving line when the transmitting line is in service.

der the control of the echo suppressorcircuits'.

', The single figure in the accompanying drawing is ,a diagrammatic view of a signal transmission system constructed in accordance with the invention.

to a four-wire line'by means of a hybrid coil 3.

The four-wire line comprises ia transmitting channel 4' and a receiving channel '5. In the transmitting channel 4 a potentiometer Bforminga part of 'a volume control apparatus is directly connected to the hybrid -coil 3. Thepo 'tentiometer Sis connected'by a transformer 1 to discharge type.

an: amplifier 8which is preferably of the space The amplifier 8 is connected through delay circuits 9, to an amplifierifl which,

delay circuit'st andamplifier it cooperate with [an echo Suppressor circuit I'l to be described lafour resistanceelements i5, '16, '11,: and I8 in series with the line and two space'discharge de- 4 devices l9 and 29 arelpreferably of the three-ele-- .ment type but it is to be understood that other types of space'discharge devicesmay be employed if so desired. The' variable repeater I4 is connected by transformers 2i and .2; to the transmitting conductors 22, and'23.

The incoming conductors 24 and.25"o'n the receiving channel are connected by transformer 26 to an, amplifier 2! which is preferably of the space discharge type. 'The amplifierZl is conarrangement 35 to af'volume limiter 3|.

The. volume limiter 31 comprises an input transformer 32, an outputtransformer 33 and.

twothree-element'space discharge devices 34 and '35 which'are effectively connected in series with the line between thesecondary windings of the two transformers 32 and 33.

/ i A normal bias is impressed upon the grids of thedevices 34 and 35 by means of 'abattery 36. A variable negative bias is impressed'upon the grids of the devices 34 and 35. according to the charge on a condenser 31. The condenser 31 is charged at times the rece iving channel 5 at a point beyond the transformer 33. The ,feed back circuit 38. comthe expander A relay is provided for blocking the out utlcf the compressor in thetransmittihg line when Preferably, the two block ing relays which selectively block theoutput circuits of the compressor and the expander are un- V be described hereinafter. 1

lexpandor' 46. position effects blocking of the receiving channel 'before the volume. limiter 3!. Thus, when sigvice 40, which serves as a detector, is biased by 'means of a battery 4| so that the feed-back cir cuit does not operate until the peaks of the signal waves on the receiving signal beyond the transj former 33 are above a predeterminedflevel. The device 40 is provided with a plate battery 42. A relay 43, which is controlled bya master echo suppressor relay 44, connects a resistance 45 in shunt to the condenser 31 when speech opa erates in the receiving line. The tendency of this shunt thus applied is to reduce'the charge on condenser 31 which in turn increases thegain J in the volume limiter 3|. The combined actions of this shunt 45 and the feed-back circuit 38 insure control of the speech volume to maintain 'a suitable volume at the output of transformer 33. :The operation of the master relay 44 will and two three-element space discharge devices 49' a and 50 which are effectively connected. inseries with the line. 'Resistance elements'5l and 52 are connected across the sections of 5 the secondary winding for the output transformer. 48. The.

cuit [4. The operation of the rectifier circuit 53 a rectifier circuit 53'which also controls the grids r of the devices [9 and $20 in' the, compressor cirin controlling the negative bias on the devices l9 and 20 in the transmitting channel 4 to com.-

press the signal volume and in controlling the negative bias on the devices 49 and in the receiving channel. 5 will be described hereinafter. The'output transformer 48 of the expan'clor 146 is connected through a pad 55 and delay circuits 56 to a spacedischarge amplifier 51. fThe am.- plifier 51 isconnected through a volumecon'trol potentiometer 58 to a space discharge amplifier The echo suppressor circuit H fcomprises a' space discharge detector tube 6| having the in,- put circuit thereofconnected across the'transmitting channel4 beyond .the amplifier ,8. The

master relay 44.-The master relay 62' when operated completes a circuit from a battery 64 V for operating relays 65,66,51, and 68. The'relays. a 65' and 66 when in released position block the transmittingchannel before and after the compressor l4. The relay 68 when in operatedposition blocks the receiving channel ,5 beyond the The'relay' 61 when in'op'erated nal waves are to be transmitted over the transmitting channel 4, the master're'lay 62 is' oper-' ated to effect operation of the relays65 and 6 6 to clear the transmitting signal and to effect operation'of the relays 61 and 68 to block the receiving channel '5. d are slow to release and have a hang-over time The relays 65, 66, and 68 'of the orderbf- 0.12 second. The relay 6! is order of0.17 second.

by a feed-back circuit 38 which is connected .to 5- Slow to release and has a hang vel. of the The operating coil for the'master'relay 44 1s "connected to the. output circuit of a space discharge detector 10. Qte'ctor, 10 is' connected across the receiving chan-. nel "5 before the limiter 3|. When the receiving The input circuit of the de- 59. The amplifier 59 is" connected through a pad 7 V 60 to the hybrid coil 3..

channel is in use, the master relay 44 is operated to complete a circuit from the battery TI to operate the relays 43 and 63. The relay 63 when operated insures against any operation of the master relay 62. This insures that the relays 65 to 68, inclusive, will be held in released position so that the transmitting channel is blocked and the receiving channel is held open.

The rectifier circuit 53 is connected to the transmitting channel beyond the compressor I 4 and to the receiving channel before the expandor 46 by means of a hybrid coil E2. The rectifier circuit 53 comprises a two-element rectifier 13 which is connected to the hybrid coil l2 by means of a transformer 14. In circuit with the rectifier 13 is a resistance element 75 shunted by condenser 16 and a biasing battery ll. Preferably, the biasing battery is of the order of 6 volts. A grid biasing battery 18 is connected to the resistance element 15 and the resistance element 15 is connected to the grids of the devices !9 and 26 in the compressor l4 and the grids of the devices 49 and 5!! in the expandor 46. The condenser 16 by-passes high frequency currents and provides a time constant so that voltage across the resistance 15 varies according to the syllabic frequency. The potential drops across the resistance element 15 act in series with the grid biasing battery 18 to cause reductions in the normal grid voltage applied to the devices i9 and 20 of the compressor M. It is apparent that the filament-to-plate impedance of the devices l9 and 26 serves as the shunt member of the H-type pad in the transmitting channel 4 and thus any reduction in the normal grid bias from the battery 18 will change the impedance of the pad and introduce loss in the transmitting channel. The constants of the rectifier circuit 53 and the devices l9 and 26 operate to give waves at the output of the compressor M which are equal to the square root of the waves appearing at the input of the compressor. Thus, in the case of speech waves, an amplitude range of about 40 decibels at the input will be compressed to a range of about 20 decibels at the output with corresponding compression for intermediate values. A more complete description of the operation of the compressor is given in the abovementioned patent to Stephen Doba, Jr., No. 2,018,489, dated October 22, 1935.

A portion of the Signal waves which pass into the expandor 66 is also impressed on the rectifier circuit 53 by means of the hybrid coil 12. The rectifier circuit 53 operates in the manner above set forth to effect reduction in the normal grid bias supplied by the battery 18 to the grids of the devices 49 and 56 in the expandor 46. The reduction in the normal grid bias on the devices A9 and 50 causes reduction in the transmission loss in the receiving channel. The combination of the actions of the rectifier circuit 53 and the devices 49 and 56 in the expandor 56 results in producing waves at the output of the expandor which are the square of the waves at the expandor input. A speech wave of 20 decibels amplitude range at the expandor input is expanded to a speech wave of 40 decibels, with intermediate values correspondingly expanded.

Briefly reviewing the operation of the system, signals received over the conductors I and 2 will be transmitted over the channel 6. The master relay 62 will be operated to eifect operation of the relays 65 and 66 to insure against any blocking of the transmitting channel 4. The relays 68 and 61 will be operated to insure blocking of the receiving channel 5. The relay 68 effectively blocks the output of the expandor 46 when the transmitting channel 4 is in use so that unbalanced currents arising from variations of the grid bias in the expandor 46 also cannot be transmitted beyond the expandor 46. The relay 66 performs a like operation with respect to the compressor I4 when the receiving channel 5 is in use.

The signal Waves passing through the compressor l4 operate the feed-back rectifier circuit 53 for effecting a compression of the waves beyond the compressor with respect to the waves before the compressor according to a fixed ratio. Preferably the Waves are compressed one-half.

Upon receipt of signal Waves over conductors 24 and 25 of the receiving channel 5 the master relay 44 is operated to eifect operation of the relay 63. The relay 63 upon operation insures against any operation of the master relay 62 which is controlled from the transmitting channel 4. Accordingly, the relays 65, 66, 67, and 68 are held in released position. This insures blocking of the transmitting channel before and after the compressor l4 so that unbalanced currents arising from variations of the grid bias in the compressor cannot disturb the operation of the system. The incoming waves on the receiving channel 5 pass through the volume limiter 3! to the output circuit thereof and if the waves are too strong, they cause operation of the gain decreaser feed-back circuit 38. This feed-back circuit begins charging of the condenser 31. The voltage built up across condenser 31 acts in series with the fixed grid bias from the battery 36 to increase the total bias and lower the gain. When the output from the volume limiter is normal, the gain decreaser circuit stops functioning. On the other hand, if the charge on the condenser 31 is too high so that the gain in the output is low,

the circuit through the resistance 45 which is' completed when relay 43 operates, causes the charge on the condenser to leak off. The circuits for charging and discharging the condenser 31 are designed so that a satisfactory input wave is supplied to the expandor 46. A portion of the waves which are supplied to the expandor 46 controls the rectifier circuit 53 to control the grid bias on the tubes 46 and 56 of the expandor 46. The expandor 46 serves to expand the waves beyond the expandor with respect to the wave before the expandor according to a fixed ratio. Preferably, the output Waves are the square of the input waves.

In the above circuit arrangement, it will be noted the rectifier circuit 53 serves as a feed-back circuit for controlling the compressor 14 and serves as a forward-acting control circuit for controlling the expandor 46. The operation of the rectifier circuit 53 in controlling the compressor i l or the expandor 46 is the same as that described in the above mentioned patent to Stephen Doba, Jr., No. 2,018,489 dated Oct. 22, 1935. In the present invention, only one rectifier circuit is required for controlling the compressor and the expandor at both ends of a four-wire line.

Modifications in the system and in arrangement and location of parts may be made within the spirit and scope of the invention and such modifications are intended to be covered by the appended claims.

What is claimed is:

1. In a transmission system, a four-wire section, an impedance in the transmitting line of the fourwire section comprising a space discharge device for variably controlling the signal volume, a space discharge device in the receiving linefor variably controlling the signal volume, and one'c'ontrol 7 when the transmitting line is in use.

circuit connected to the transmitting and receiving lines andrectifyingaportion of the signals on each of said lines forlgoverning the grid bias I impressed on said devices to control the volume" beyond said devices in the transmitting and "re- 7 eceiving lines.

2. In a transmission systemhavinga. four yi rire section, an impedance in the transmittingli'neo'f -the four-wire section comprising a space dischargedevice for controlling the signal volume, a

space "discharge device in the receiving line for controlling the signal volume, means comprising one rectifier circuit'connected to the transmittingand receiving lines. and rectifying a portion of the signals on each of said lines for controlling the grid bias impressed onsam devices tocontrol the volume beyond said devices in thetransmit- "ting and receiving lines, and-means for blocking the output circuit 'o'f the device in one line when i the other line is muse.

3. In a transmission system having a'four-wire section,; compressing means in the transmitting line forvariably'compressing the volume range of the signals, expanding, means in the receiving line for variably expanding thevolume range of the signals, a 'hybrid coil connected between the transmitting and receiving lines, said hybrid coil being connected to the transmitting linebeyond the compressing means therein and to the receiving therein; and means comprising a rectifying circuit connected to said hybrid coil forcontrolling said compressing means and saidgexpanding means.

4. In a transmission system; a four' wire sec 7 tion, means in'the transmitting line for variably compressing the volume range of the" signals," means in the receiving line for. variably expanding the volume range of the signals, means com-' prising one rectifying circuit connected to the transmitting and the receiving lines and rectify- 7 ing'a'portionof the signals on each of said lines forcontrolling said compressing means and said expanding means respectively by the signals on the transmitting and receiving'lines; and means for blocking "the output :from the compressing means when the receiving line is'inuse and for "blocking the output from th'e' expanding means '5. ma transmission'system having a four-wire section, compressing means in. the transmitting line for variably compressingthe volume range f the signals, expanding means in' the receiving line for variably expanding the volume range of r the signals, a hybrid coil connected to the transmitting line beyond said compressing means and to the receiving line before 'sa'idexpanding means, 7

means comprising a rectifying circuit connected to said hybrid coil for controlling said compressing means and said expanding means, and means for blocking the output from the compressing means when, the receiving line is in use and for blocking the output from the expanding means when the transmittingline'is in use.

6;jIn' a transmitting's'ystem, a four-wire section, an impedance pad inthe transmitting line of the four-wire section having a space discharge device connectedacross it,'a space discharge de-: vice connected effectivelyin series with the receiving line of said four-wire-section, and one 'rectifying circuit connected to the transmitting linean'd to the receiving'line andVrectif-ying a 'portion of the signals on each of said lines for 1 line before the expanding means 2,Q84,457 V, V I

controlling the device in the transmitting line and'the' device in the receiving line, said rectifying circuit having a characteristic with a definite relationwithrespect to the'characteristics of the devices in the transmitting and receiving lines for effecting a compression of the volume range on the transmittingline beyondsaid pad with respect to the volume range beforethe pad accord-- ing to'a fixed ratio 'and'fo'r, effecting an expan sion, o'f'the volume range beyond thedevice in V the receiving line with respect to the volume range before the last mentioned device-according toafix'ed ratio; 3

f '7. In a'tra'nsmitting system, a 'fourwiresection, an impedance pad in the transmitting line device connected across it,.a space discharge dervice connected effectively in series with the ref 'ceiving line of said four-wire 'section,-means comprising a single rectifying circuit" connected to'thetransmitting line and to the receiving line and rectifying a portion of the signalson each of 7 said lines for controlling the device in the transmitting line and the devicein the receiving line respectively 'by' the signals on the transmitting and receiving lines, said rectifying circuit-having a characteristic with a definite relation with respect to the characteristics of the devices in the transmitting and receiving lines for effecting a compression ofthe volume range on they trans- "mitting line beyond said pad with respect to the volume rangebefore the pad according to a fixed j ratio and for effecting an. expansion of the vol: ume range beyond the device in the receiving line with respect to the vQlumerangebefore the last mentioned device according to agfixed ratio,

and means'for blocking'the output circuit of the line is in'use and for blocking the output circuit of the device in the transmitting line when the receiving line is in use.

8. In a transmission'systern, a four-wire section, an impedancepadinthe transmitting line said pad and to theireceiving line before said devices, and means comprising a rectifying circuit connected to said hybrid coil for impressing 5 device inthe, receiving line when the transmitting a biasing potential on the grids of the devices in the transmitting line to compress the volume.

range beyond the pad with respect to thevolume range before the pad according to a fixed ratio and for impressing a biasing potential on the grids of the devices in the receiving line to expand the volume range beyond the devices in n the receiving line with respectto the volume ratio. 7 I a 9. In a transmission system, a four-wire section, an impedance pad in the transmitting line of said four-wire section, two space discharge devices in push-pull relation connected across range before said deviceaccording toafixed" said pad, twospace discharge devicesin push v pull relation effectively connectedin series with .the receiving line of said four-wire section, a' hybrid coil connected to the transmitting linebeyond said pad and to the receiving line before :said devices, means comprising a rectifying-cit cuit connected to said hybrid coil for impressing ,abiasing potential 'on the'grids of the devices in the transmitting line to compress the volume 15 ,of the-four wire section having a space discharge;

range beyond the pad with respect to the volume range before the pad according to a fixed ratio and for impressing a biasing potential on the grids of the devices in the receiving} line to expand the volume range beyond the devices in the receiving line with respect to the volume range before said devices according to a fixed ratio, and means for blocking the output circuits of the devices in the transmitting line when the receiving line is in use and for blocking the output circuits of the devices in the receiving line when the transmitting line is in use.

10. In a transmission system, a four-wire sec tion connected to a two-wire section, a space discharge device connected across a pad in the transmitting line of the four-wire section, a space discharge device connected effectively in series with the receiving line of the four-wire section, a control hybrid coil connected to the 20 transmitting line of the four-wire section beyond said device in the transmitting line and to the receiving line of the four-Wire section ahead of said device in the receiving line, means comprising a rectifying circuit connected between said control hybrid coil and the grids of the devices in the transmitting and receiving lines for obtaining a variation in volume range beyond the device in the transmitting line with respect to Volume range input thereto according to a fixed ratio and for obtaining a variation in vol-' ume range beyond the device in the receiving line with respect to the volume range input thereto according to a fixed ratio, and means for blocking the output circuit of the device in the transmitting line when the receiving line is in service and for blocking the output circuit of the device in the receiving line when the transmitting line is in service.

LIONEL SCHOTT. 

